The proposed research is directed toward understanding how the DNA sequence of a bacterial promoter determines its transcriptional activity. Promotor activities will be measured in vivo using a standardized system in which a DNA restriction fragment containing a promoter is oriented by in vitro recombinant techniques so as to produce expression of an easily assayed gene. The promoters examined will be a collection of well characterized promoters including a number of variations of the tryptophan operon promoter. A number of in vitro constructions will be undertaken to provide promoters with specific sequence alterations designed to test current models dealing with the relationship of DNA sequence to promoter function. In addition, the response of various promoters to growth conditions will be examined in an effort to establish what aspect of promoter structure is involved. Studies of the interactian of RNA polymerase with a number of promoters in vitro are planned to correlate the in vivo observations with particular features of the interaction of RNA polymerase with the promoter DNA in vitro. By some knowledge of the role that different parts of the promoter sequence play in specifying the transcription initiation frequency from a given promoter, we will gain some understanding of how the level of expression of a large number of bacterial operons is determined and coordinated during cell growth.